The present invention relates to a method and system for controlling a cooperative object-transporting robot usable in heavy article transport operations in the mining and manufacturing industries, the agriculture, forestry, and fishery industries, the construction industry, the distribution industry, homes, etc.
One of object-transporting methods in which a man and a robot cooperatively transport an object, is a method called xe2x80x9cpower assistxe2x80x9d which has been studied by the California University, the Tohoku University, the Mechanical Engineering Laboratory of the Agency of Industrial Science and Technology, etc. This is a technique in which there are provided two force sensors for detecting the load of an object grasped by the tip of a robot arm and a force applied by an operator, respectively, and in which the robot reduces the load of the operator while moving so as to copy after the motion of the operator, by amplifying the force applied by the operator and then applying the amplified force to the object.
However, in accordance with this method, it is necessary for the operator to grasp a force sensor handle disposed at the tip of the robot arm and to move it, and hence the place where a force can be applied is limited to only one portion of the object. When transporting a long object or a large-sized object, as shown in FIG. 1, it is desirable that a hand 2 attached at the tip of the robot arm 1 and a human operator 3 grasp, for example, each of the ends of the object 4 and support the object 4. However, in this case, while a force can be measured on the robot arm 1 side by providing a force sensor 5, a force applied to the object 4 cannot be directly measured on the operator 3 side. This makes it difficult to apply the above-described xe2x80x9cpower assistxe2x80x9d technique.
On the other hand, the Stanford University in U.S., the Tohoku University, etc. has studied a method in which a man and a robot support an object at some portions thereof and in which they transport the object while sharing the load therebetween. This method is primarily based on impedance control. Specifically, in this method, an object is supported under weightless conditions by compensating for the weight of the object, and simultaneously virtual impedances (inertia, viscosity, and spring coefficient) are set with respect to the object or the robot, whereby the motion of the object is changed in response to the change in the force applied by the man, and the motion of the object is caused to copy after the motion of the man.
In order to compensate for the gravity acting on the object, however, it is necessary to know in advance the mass or the mass distribution of the object. This hinders this method from being flexibly applied to the transportation of various objects.
When the object is a long object, it is virtually only a translational force which a man can apply. It is difficult to apply a torque (rotational force) to one end of an object to be transported. In the case of a control based on impedance control, a straight-ahead motion in the direction of the long axis obtained by connecting the man and the robot is easy, but with regard to a motion including rotation, it is difficult for man to positionally control the end point of the robot side as a target point. In order to move the body by applying a small force, it is necessary to set impedance parameters such as inertia and viscosity to be low values. In this case, however, a drift (slipping motion) in the normal direction is generated, and the drift is difficult to stop. This raises a problem that it is difficult to intuitively forecast behavior of the object.
The reason that the above-described problems associated with the conventional art is caused is because the impedance parameters are set to be uniform in all directions, and also they are set to be in an absolute coordinate space. As a result, behavior of the object becomes one which man has never daily experienced, so to speak, a case like as if the object floating in a weightless space were moved by a force applied. This makes operations of making the object reach a target position and posture difficult.
It is an object of the present invention to solve the above-described problems, and to achieve a controlling means for making the arm of a cooperative object-transporting robot share approximately a half of the weight of an long object, in the robot control in which a man and the robot grasp each of the ends of the long object, sharing the load due to the weight thereof.
It is another object of the present invention to achieve a controlling means for a cooperative object-transporting robot, the controlling means having only to have one sensor for measuring a force applied to the robot arm by an object, as a force sensor, without the need to have a sensor for measuring a force by an operator, and the controlling means not being required to know the dimensions and the mass of the object in advance.
It is still another object of the present invention to permit a man to intuitively perceive the behavior of the object by the daily senses thereof in the control for the above-described cooperative object-transporting robot, by simplifying the relationship between the force applied by the man and the motion of the object by limiting the direction in which the object is movable.
It is a further object of the present invention to achieve a controlling means for a cooperative object-transporting robot, the controlling means permitting a man to intuitively perceive the above-described behavior of the object by the daily senses, without deviating from the original operational purpose of making the object reach arbitrary target position and posture.
In order to achieve the above-described purposes, the controlling method in accordance with the present invention, which is essentially a controlling method for controlling the cooperative object-transporting robot in order that a man and the robot transport a long object or a large-sized object while grasping each of the ends thereof, is characterized in that an angle of the hand-tip of the robot is detected by angle sensors, and that, based on the sensor signals, a motion instruction for a translational motion of the hand-tip in the vertical direction is output so as to keep the posture of the object horizontal.
The above-described controlling method may be such that a force applied to the robot by the object and an angle of the hand-tip of the robot are detected by sensors, and that, based on the sensor signals, a motion instruction to drive the robot arm is output for the rotational motion component around the horizontal axis and the translational motion component in the horizontal back-and-forth direction, upon setting a gain so as to reduce the resistance forces of the robot to small values.
On the other hand, the controlling system in accordance with the present invention is essentially a controlling system for controlling the cooperative object-transporting robot in order that a man and the robot transport a long object or a large-sized object while grasping each of the ends thereof, and is characterized by angle sensors for detecting an object-grasping angle of the hand-tip of the robot, a motion converting part for outputting the motion component of the hand-tip in the vertical direction so as to keep the posture of the object horizontal, based on the hand-tip angle detected by the angle sensors, and a coordinate converting part for outputting a motion instruction to drive the robot arm, based on the above-mentioned motion component.
The above-described controlling system may comprise a force sensor for detecting a force applied to the robot by the object, a coordinate converting part for separating the rotational force component around the horizontal axis and the translational force component in the horizontal back-and-forth direction, from the sensor signal of the force sensor, a force-motion converting part for outputting these motion components, using a gain such as to reduce the resistance forces of the robot in these rotational direction and translation direction to small values, based on the above-mentioned two force components, and a coordinate converting part for synthesizing these motion components and outputting a motion instruction to drive the robot arm.
In accordance with the controlling means for the cooperative object-transporting robot having the above-described constitution, when controlling the cooperative object-transporting robot which is arranged so that a man and the robot grasp each of the ends of the object, and that they transport the object sharing the load due to the weight thereof, it is possible to control so that the robot arm shares approximately a half of the weight of the object, by controlling the translational motion of the hand-tip in the vertical direction so as to keep the posture of the object horizontal. Simultaneously, it is possible to control the rotational motion of the hand-tip of the robot so that the rotational force at the hand-tip thereof becomes zero. As a force sensor, it is essential only that one sensor for measuring a force applied to the robot arm by an object is provided. There is no need for sensor for measuring a force by an operator. Also, it is unnecessary to know in advance the dimensions and the mass of the object.
Next, a second controlling method is a controlling method for controlling the cooperative object-transporting robot in order that a man and the robot transport a long object or a large-sized object in a horizontal plane while grasping each of the ends thereof, and is characterized in that a force applied to the robot by the object is detected by a force sensor, and that, based on the rotational force component around the vertical axis, and the translational force component in the direction of the object long axis obtained by connecting the point grasped by the man and the point grasped by the robot, each of which is separated from the sensor signal, the above-mentioned rotational motion component around the vertical axis and the above-mentioned translational motion component in direction of the object long axis are output, upon setting a gain so as to reduce the resistance forces of the object to small values, while the translational force component in the direction of the object short axis orthogonal to above-mentioned object long axis is constrained so that no translational motion in the direction of the object short axis occurs, whereby a motion limitation equivalent to the object being supported by a virtual wheel facing the direction of the object long axis, at one point on the robot side, is imposed on the object, and then the robot arm is driven. Furthermore, in such a controlling method, the control may also be performed on the precondition that an angle of the hand-tip of the robot is detected by angle sensors, and that, based on the sensor signals, a motion instruction for a translational motion of the hand-tip in the vertical direction is output so as to keep the posture of the object horizontal.
Moreover, a second controlling system is a controlling system for controlling the cooperative object-transporting robot in order that a man and the robot transport a long object or a large-sized object in a horizontal plane while grasping each of the ends thereof, and is characterized by a force sensor for detecting a force applied to the robot by the object, a coordinate converting part for separating, from the sensor signal, the rotational force component around the vertical axis, the translating force component in the direction of the object long axis obtained by connecting the point grasped by the man and the point grasped by the robot, and the translating force component in direction of the object short axis orthogonal thereto, a force-motion converting part which, based on the above-mentioned rotational force component around the vertical axis and the above-mentioned translational force component in the direction of the object long axis, outputs these motion components, using a gain such as to reduce the resistance forces of the robot in these rotational direction and translation direction, and a coordinate converting part for synthesizing these motion components and the above-mentioned translational force component in the direction of the object short axis which is set to be zero, and outputting a motion instruction to drive the robot arm.
In accordance with the controlling means for the cooperative object-transporting robot having the above-described constitution, when controlling the cooperative object-transporting robot which is arranged so that a man and the robot transport a long object or a large-sized object in the horizontal plane while grasping each of the ends thereof, a motion limitation equivalent to the object being supported by a virtual wheel facing the direction of the object long axis, at one point on the robot side, is imposed on the object, and thereby the direction in which the object is movable is limited. This simplifies the relationship between the force applied by the operator and the motion of the object, and permits the operator to intuitively perceive the behavior of the object by daily senses thereof. In addition, there is no fear of deviating from the original operational purpose of making the object reach arbitrary target position and posture.